Structural and vibrational properties of imidazo[4,5-c]pyridine, a structural unit in natural products.

The molecular structures and vibrational properties of 1H-imidazo[4,5-c]pyridine in its monomeric and dimeric forms are analyzed and related to the experimental results derived from the XRD, IR, and Raman studies. The theoretical data are discussed on the basis of DFT quantum chemical calculations using the B3LYP correlation functional and 6-311G(2d,2p) basis set. This compound crystallizes in the non-centrosymmetric orthorhombic space group Fdd2. The asymmetric unit contains one molecule of 1H-imidazo[4,5-c]pyridine and disordered molecules of solvents. The molecules are organized in hydrogen-bonded chains propagating along the [1 0 -3] direction. The stability of the dimeric form arising from charge delocalization and the existence of an N-H···N intermolecular hydrogen bond has been analyzed using the natural bond orbital approach. The normal modes, which are unique for the imidazopyridine skeleton, have been identified. The spectra of other compounds containing the imidazopyridine unit have been analyzed.